# E=mc^2 homework problem

1. Jan 14, 2010

### majormuss

1. The problem statement, all variables and given/known data
A tritium nucleus is formed by combining two
neutrons and a proton. The mass of this nucleus
is 9.106 × 10–3 universal mass unit less than the
combined mass of the particles from which it is
formed. Approximately how much energy is
released when this nucleus is formed?
(1) 8.48 × 10–2 MeV (3) 8.48 MeV
(2) 2.73 MeV (4) 273 MeV

2. Relevant equations

E=mc^2

3. The attempt at a solution
I tried finding the energy by using what they gave me(9.106 × 10^-3) and fixing into the equation E=mc^2, but my anwser turns out 8.2 × 10^13( which obviously missing something)

2. Jan 14, 2010

### sylas

Re: E=mc^2

Think about what units you are using. You may need to convert units.

3. Jan 14, 2010

### vela

Staff Emeritus
Re: E=mc^2

You can't just plug the numbers you have in and get the right answer because the units don't work out.

4. Jan 14, 2010

### majormuss

Re: E=mc^2

so how do I change form Joules to Mega Electron Volts? do I multiply or divide by 1.6 *10^-19... that is where I tend to get confused.

5. Jan 14, 2010

### Matterwave

Re: E=mc^2

Is a joule larger or smaller than a MeV?

So if I have 1 joule, should have 1*1.6*10^-13 MeV or 1/(1.6*10^-13) MeV? Which one gives a bigger answer?

Also, for mega electron volts the conversion factor is 1.6*10^-13 not -19, -19 is for electron volts.

6. Jan 15, 2010

### sylas

Re: E=mc^2

You also need the mass units to be right.